Editor of Newsnight, Ian Katz, said: "While we would not seek to obstruct any police investigation we are concerned that the use of the Terrorism Act to obtain communication between journalists and sources will make it very difficult for reporters to cover this issue of critical public interest."

A BBC spokeswoman said: "Police obtained an order under the Terrorism Act requiring the BBC to hand over communication between a Newsnight journalist and a man in Syria who had publicly identified himself as an IS member. The man had featured in Newsnight reports and was not a confidential source".

Police have far-reaching powers under Section 32 of the Terrorism Act 2000 which deems any police inquiry into the "commission, preparation or instigation of acts of terrorism" to be termed a "terrorism investigation".

Kermani, who has previously worked for BBC London, Channel 4 News and the Islam Channel, was criticised last year for a Newsnight interview with a British-born IS fighter.

"Awlaki", a 27-year-old British Pakistani fighter, told Kermani he hated the UK and joked about the group beheading its enemies.

Conservative MPs Michael Ellis and Nigel Evans lambasted the BBC programme for running the interview, saying it gave the group a mainstream media platform.

Kermani developed contact with Awlaki over several months and said the jihadi was "softly spoken". The BBC said the report "offered insights" into IS crimes.